I am actually going to break this discussion up into four separate posts because of the depth of the subject area and the investment Microsoft has made in the features. The work that Microsoft has done to enable social bookmarking and tagging within SharePoint 2010 is both broad and deep, and a single blog post on the subject would be too long.
Here is how I am going to break up Part 5 of my series into four blog posts:
Part 5a - Intro and Central Database of Bookmarks and Tags For All Users < You are here
Part 5b - Bookmarking and Tagging User Experience
Part 5c - Browsing Bookmarks and Tags
Part 5d - Searching Bookmarks and Tags